1. Field of the Invention
The present invention relates to a thermosensitive transfer film used to form a phosphor screen in a display, such as a color cathode ray tube or the like, and to a method of using the film.
2. Description of the Related Art
In recent years, as the color cathode ray tube is becoming larger and its screen is becoming flatter, there is an increased demand for enhanced contrast and color purity in the quality aspect and the like.
Consequently, various constructions to enhance the contrast have been proposed.
FIG. 6 is a schematic diagram showing phosphors of three colors formed on a panel glass of a color cathode ray tube.
On a panel 50, phosphor layers 51B, 51G and 51R, corresponding to the three colors blue, green and red, respectively, are disposed, and a light absorbing layer 52 made of carbon is formed between the phosphor layers 51B, 51G and 51R.
In FIG. 6, the transmittance of the panel 50 is set as T, and intensities of light emitted to the phosphor layers 51B, 51G and 51R are set as LB, LG and LR, respectively.
With attention to the center phosphor layer 51G of green, when the reflectance of external light having an intensity of LO applied to the green phosphor layer 51G is RG, the intensity (corresponding to luminance) of transmission light L1 is expressed as LGxc3x97T, and the intensity of reflection light L2 of the external light is expressed as LOxc3x97Txc3x97RGxc3x97T. Similar expressions apply for the other phosphor layers 51B and 51R.
In this case, the contrast can be expressed as follows.
Contrast
=intensity of transmission light L1/intensity of reflection light L2 of external light
=LGxc3x97T/LOxc3x97TRGxc3x97T=LG/LOxc3x97RGxc3x97T
From the equation, it is understood that, in order to enhance the contrast, first, the transmittance T of the panel 50 has to be reduced.
For example, the method of enhancing the contrast by coloring the panel glass to reduce the reflection of external light has been considered. A color cathode ray tube of a high contrast using a dark glass and having a transmittance T of 40 to 50% as the panel glass has been commercially available.
The method of enhancing the contrast by using the dark glass is, however, equivalent to form, so to speak, a black filter. It is not preferable, since light emission of the phosphor is absorbed by the panel glass and the luminance deteriorates.
In addition; the method of enhancing the contrast by adhering a pigment of the same color as that of the phosphor to the surface of a phosphor particle has been proposed. By this method as well, since light emitted by the phosphor is absorbed by the pigment of the same color, the luminance deteriorates.
Methods of providing a color filter of the same color as that of the light emitted by the phosphor between the panel glass and the phosphor layer have been proposed (refer to Japanese Unexamined Patent Application Nos. 64-7457, 5-275006, 5-266795, 9-274103 and the like).
Specifically, as shown in FIG. 7, color filter layers 53B, 53G and 53R, having the same colors as those of the phosphor layers 51B, 51G and 51R, are formed under the phosphor layers 51B, 51G and 51R, respectively.
By forming the color filter layers 53B, 53G and 53R, the transmittance is obtained from the transmittance T of the panel glass 50 and the transmittances from each of the color filter layers 53B, 53G and 53R, so that the resultant transmittance is slightly lowered.
In this case, although the luminance also is slightly lowered, the reflectance RG is lowered more than that by the color filter layers 53B, 53G and 53R. The intensity of the reflection light L2 is, therefore, suppressed and the contrast ratio can be improved.
By this method, therefore, both color purity and contrast can be largely improved.
When compensating for the reduction in the luminance due to the formation of the color filter layers 53B, 53G and 53R, the intensities of the electron beams LB, LG and LR are raised.
In the case of providing the color filter layers, it is necessary to perform the process of forming the color filter layers by a slurry method and, after that, the process of forming phosphor layers on the color filter layers by using the slurry method.
The slurry method is a method comprising the steps of preparing a slurry in which a material of either a color filter layer or a phosphor layer and a photosensitive component are dispersed, applying the slurry, drying the slurry to form a layer, and patterning the layer by exposure and development, thereby forming a color filter layer or a phosphor layer in a predetermined pattern.
In the case of forming a red color filter layer, since ferric oxide (transparent red oxide) and cadmium sulfoselenide used as red pigments absorb ultraviolet rays at the time of exposure, the red color filter layer is not sufficiently set in the thickness direction, and the pattern loses its shape by the development. The red color filter layer, therefore, cannot be patterned by the slurry method.
The red color filter layer has to be formed by using the so-called inversion development.
Specifically, after a resist layer is formed on the whole surface, the resist layer is patterned by exposure and development so that the parts (blue pixels, green pixels and carbon strips between them), expect for red pixels remain.
On the whole surface, a slurry containing the material of the red color filter is applied and dried.
After that, both the resist layer and the material of the red color filter on the resist layer are lifted off. Consequently, the red color filter layer can be formed only in areas of the red pixels where there is no resist layer.
As described above, in order to mount the color filter to the color cathode ray tube, in addition to the manufacturing processes of the color cathode ray tube on which no color filter is mounted, a large number of processes are necessary. Consequently, there are the drawbacks that the work is very complicated and the manufacturing cost is high.
Moreover, in the manufacturing process, the processes of slurry application, drying, exposure, development and drying of a pattern are added. Since this increases the burden on the carbon strips 52 that are already formed before the color filters are formed, the linearity of the edges of the pixels obtained deteriorates, a defect occurs due to a break, and a defect due to adhered dust or trapped foreign matter also occurs.
When polyvinylalcohol (PVA) - ammonium dichromate (ADC), polyvinylalcohol (PVA) - sodium dichromate (SDC) or the like as a photosensitive component is used for a slurry for a color filter, a large amount of drainage containing chrome is generated in the manufacturing process. This causes the problem of a high cost for drainage disposal.
To deal with the problems, the invention provides a thermosensitive transfer film of which the color filter layer and the phosphor layer can be formed easily with a small number of processes, a method of using the film, a method of manufacturing a display, and a method of manufacturing a cathode ray tube.